1. Field of the Invention
The present invention relates to a refrigerating system and more particularly to a pulse tube type refrigerating system.
2. Description of the Prior Art
The pulse tube type refrigerating system has been first proposed in 1963 by W.E. Gifford et al. and known as a system which can produce a low temperature below 200.degree. K. without using a movable mechanism which are to be operated under a low temperature. This type of refrigerating system has been recognized as being characterized by a simple structure and a high reliability. The refrigerating system is based on the principle which utilizes property of the working fluid under inequilibrium. Therefore, analysis of the operation of the system through equations is rather difficult. In the past, there have been developed various theories for analyzing the mechanism for producing cold temperature in the pulse tube refrigerating system, however, such theories are based on various assumptions so that the operating principle is not clearly analyzed.
A typical example of the pulse tube refrigerating system is shown in FIG. 5. There is a compressor 1 having an output port connected with a discharge line 1a and a suction port connected with a suction line 1b. The discharge line 1a is connected through an discharge valve 2 with a regenerator 3. The suction line 1b is connected with the regenerator 3. The regenerator 3 is connected with a refrigerating section 4 which is in turn connected with one end of a pulse tube 5 having a hollow interior 6. The other end of the pulse tube 5 is connected with a heat exchanger 7 of an appropriate type. Within the system, there is contained a working fluid such as helium, argon, nitrogen, hydrogen or a mixture of one of these fluids and air.
In the discharge line 1a, the working fluid is compressed adiabatically by the compressor 1 to a pressure of approximately 15 atms. In this stage, the working fluid is increased in temperature due to the adiabatic compression. The working fluid under pressure is then passed through an intake valve 2 into the regenerator 3 where it gives thermal energy to a medium in the regenerator 3. The working fluid is thus decreased in temperature in the regenerator 3 and introduced through the refrigerating section 4 into the pulse tube 5.
The pulse tube 5 contains working fluid and this working fluid is compressed adiabatically by the pressurized fluid from the regenerator 3 to be increased in temperature. The working fluid which has been in the pulse tube and compressed by the fluid from the regenerator 3 is then passed to the heat exchanger 7 to radiate heat into atmosphere or another medium at atmospheric temperature.
Thereafter, the outlet valve 8 is opened so that the working fluid in the system is allowed to flow through the suction line 1b into the compressor 1. In this stage, the working fluid in the heat exchanger 7 is returned to the pulse tube 5 to thereby expel the working fluid in the pulse tube 5. The working fluid returned from the heat exchanger 7 to the pulse tube 5 is then expanded to be decreased in temperature. The working fluid thus decreased in temperature is passed to the refrigerating section 4 to cool the medium around the section 4. With this working cycle, the medium around the refrigerating section 4 can be cooled down. There will be a temperature gradient along the length of the pulse tube 5 from the refrigerated temperature to the temperature of the heat exchanger 7. As an example, the temperature at the refrigerating section 4 is approximately 77.degree. K. whereas the temperature at the heat exchanger 7 is approximately 320.degree. K.
In the working stage wherein the outlet valve 8 is opened, there is a time difference between the timing wherein the working fluid which has remained in or in the vicinity of the regenerator 3 expels the fluid in the suction line 1b and the timing wherein the working fluid in the heat exchanger 7 is moved to the pulse tube 5. In other words, there is a difference in phase in the movement of the working fluid through the outlet valve 8 and the movement of the working fluid in the pulse tube 5. It is understood that this phase difference produces the refrigeration at the section 4.
It has been found that the conventional pulse tube type refrigerating system is disadvantageous in that the efficiency is very low as compared with other types of refrigerating systems. In a conventional pulse tube type refrigerating system, an output of 2 W under 77.degree. K. can be obtained with an input of 1 kW. Thus, the conventional system shows a performance number 1000/2=500.